Scenario Earthquake Shaking Maps in Japan

Nobuyuki Morikawa

National Research Institute for Earth Science and Disaster Prevention (NIED), JAPAN

Example of SESMs

The Kego fault zone (south-east part)

・・・ The first application of the revised-version of ‘Recipe’

Characterized source model Fault length (L) by the long-term evaluation ⇒ Outer source parameters

(Added to the revised-version of ‘Recipe’)

Formulae

M = (log L +2.9) / L

(4) log M0 = 1.17・M + 10.72

(2)’ S = 2.23・10-15・(M0×107)2/3 (M≧7)

(3)’ S= 4.24・10-11・(M0×107)1/2 (M<7)

(5) W = S / L

(6) Lmodel = S / Wmodel

(7) Smodel = Lmodel・Wmodel

Characterized source model Outer source parameters ⇒ Inner source parameters

For details, see ‘Recipe’

(http://www.j-shis.bosai.go.jp/map/JSHIS2/text/news_en.html)

Deep sediments structure model

(Vs=1.1km/s) (Vs=1.4km/s) (Vs=1.7km/s)

(Vs=2.1km/s) (Vs=2.7km/s) (Vs=3.1km/s)

Seismic bedrock (Vs=3.1 km/s) ～ engineering bedrock (Vs = 0.6 km/s)

Results-1 Peak velocity distribution on the engineering bedrock

・ peak velocities at

near source fault in

cases 1a and 1b are

larger than cases 2a

and 2b

・ large peak velocity

region extends to

southeastern of the

source fault in cases 1b

and 2b

(forward directivity

effect and

amplifications by

sediments)

Results-2 Comparison of calculated peak velocity on the engineering bedrock

with an empirical attenuation relation by Si and Midorikawa (1999)

・ Calculated peak

velocities have a

tendency small

compared with the

attenuation relation. The

depth to seismic bedrock

is shallow (200m or

less) at most of the

calculated region.

・ Forward directivity

effect and amplifications

by sediments causes

some large velocities in

cases 1b and 2b.

Results-3 Examples of velocity waveforms on the engineering bedrock

(point A: Locate just on the source fault)

○ cases 1a & 1b (1 asperity model)

large amplitudes with short duration

○ cases 2a & 2b (2 asperities model)

relatively small amplitudes with long

duration

Results-4 Examples of velocity waveforms on the engineering bedrock

(point C: Located in a direction extending from the source fault)

○ cases 1a & 2a

small amplitudes

○ cases 1b & 2b

large pulse with period of about 3s

(forward directivity effect

+ amplification by sediments)

Results-5 Examples of velocity waveforms on the engineering bedrock

(point E: Located on very thick sediments)

○ all cases

remarkable later phases with large

amplitudes and periods of 5s

○ cases 1b & 2b

relatively large amplitude

(forward directivity effect)

Calculation of JMA seismic intensity

(IJMA) on the ground surface

Waveforms on the

engineering bedrock

IJMA on the engineering

bedrock

IJMA on the ground

surface

Engineering

geomorphologic

classification

Amplification factor

for peak velocity

Site amplification factor

for IJMA

Relation between

peak velocity and IJMA

Consideration of surface structure

(engineering bedrock ～ ground surface)

Average S-wave

velocity up to 30m

depth (AVS30)

Surface structure model

Site amplification factor for IJMA from engineering bedrock (Vs=0.6km/s)

to the ground surface

Engineering

geomorphologic

Classification

(Wakamatsu &

Matsuoka, 2008)

Amplification

factor for peak

velocity

(Fujimoto &

Midorikawa, 2006)

AVS30

(Matsuoka &

Wakamatsu,

2008)

Results-6 JMA seismic intensity distribution on the ground surface

・ Large amplification

in basins causes very

large JMA seismic

intensity on the ground

surface for all cases.

・ Difference between

basin and mountain

regions is more

remarkable compared

with peak velocity on

the engineering

bedrock.

IJMA

Conclusions Scenario Earthquake Shaking Maps

・・・can understand strong ground motion distribution if the target

earthquake occurs,

・・・are considered the influences of the rupture processes of the

source fault and detail underground structure, especially the deep

sedimentary layers structure.

Problems remain:

・ It is not enough to consider uncertainties in strong-motion

evaluations because only one or few cases are carried out for a target

major active fault.

・The underground structure models should be improved much more.

・SESMs for large subduction-zone earthquakes are also required.

・Forward directivity effect may be overestimated because simple

rupture propagation (circular rupture propagation with a constant

rupture velocity) is assumed in the simulation.

Thank you for your attention !